The present invention relates to a semiconductor device with an array of three-terminal type light emitting elements such as light emitting thyristors, an optical print head using such a semiconductor device, and an image forming apparatus using such an optical print head.
An image forming apparatus such as a printer, a copier, a facsimile machine or a combined machine includes an optical print head with an LED (Light Emitting Diode) array chip (i.e., a semiconductor device).
The LED array chip includes a plurality of LEDs linearly arranged on a substrate, a common wiring portion connected to external driving circuits for driving the LEDs, and a lead-out wiring portion for connecting the LEDs and the common wiring portion.
Patent Document 1 discloses a technique in which a semiconductor epitaxial film (including a light emitting layer) is bonded onto a substrate using intermolecular force, and then the semiconductor epitaxial film is fabricated into the LED array on the substrate. The substrate has a common wiring portion (i.e., a driving IC region) formed thereon before the semiconductor epitaxial film is bonded onto the substrate. The LEDs and the common wiring portion are connected using the lead-out wiring portion (i.e., individual electrodes) extending in a direction perpendicular to an arranging direction of the LEDs.
Patent Document 1: Japanese Laid-open Patent Publication No. 2006-237303 (see, FIGS. 1, 8 and 11).
Recently, there has been developed a light emitting thyristor array chip including light emitting thyristors instead of the LEDs.
The light emitting thyristor has three terminals (i.e., an anode, a cathode and a gate), while the LED has two terminals. Therefore, the light emitting thyristor array chip has larger number of wirings and electrodes (for connecting the light emitting thyristors and the common wiring portion) than those in the LED array chip.
Recently, there is a demand for a technology capable of reducing a possibility of short circuiting, and capable of preventing an increase in size of the light emitting thyristor array chip.